<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>表达式与操作符</title>
</head>
<body>
    <script>
        var a, b,s;
   a= Number( prompt("请输入三角形的底边长度"))
   b= Number( prompt("请输入三角形的高"))
   s=1/2*a*b;
   alert('三角形的面积为'+s)
    </script>
</body>
</html>